Temperature-dependence parameters for CH3I-O2 and CH3I-air line-broadening coefficients

Abstract

Taking advantage of the temperature-invariant semi-empirical model parameters determined previously at room temperature [JQSRT 273, 107839 (2021)], CH3I-O2/air line-broadening coefficients in the interval 200–400 K recommended for HITRAN are calculated for the R,PP, R,PQ and R,PR sub-branches of the ν6 band and a large range of quantum numbers (0 ≤ J ≤ 70, K ≤ 20) generally requested by spectroscopic databases. These theoretical estimates are further used to extract the associated temperature-dependence parameters. As perfectly linear fits in log-log coordinates are obtained with the traditional power law, the deduced temperature-dependence exponents ensure an accurate description of the line-broadening coefficients at any temperature in the considered temperature range and more advanced models such as double-power law are not applicable. Since no not-room temperature measurements are currently available, these data can be extremely useful for terrestrial-atmosphere applications involving methyl iodide. The values computed for the ν6 band can be also used as reasonable estimates for other parallel and perpendicular bands due to the negligible sub-branch dependence and weak vibrational dependence.